static <A> A addAndReturnIfNotNull(Collection<A> l, A a) {
  if (a != null && l != null) l.add(a);
  ret a;
}

ifclass MultiSet
static <A> A addAndReturnIfNotNull(MultiSet<A> ms, A a) {
  if (a != null && ms != null) ms.add(a);
  ret a;
}
endif